Question? Just ask us!
Free Encyclopedia of Building & Environmental Inspection, Testing, Diagnosis, Repair
InspectAPedia ® Home
WATER PUMPS, TANKS, TESTS, WELLS, REPAIRS
CHEMICAL CONTAMINANTS in WATER
DRINKING WATER TESTING
DRINKING WATER - EMERGENCY PURIFICATION
PLUMBING SYSTEM INSPECT DIAGNOSE REPAIR
WATER CONSERVATION MEASURES
WATER CONTAMINANT LEVELS
WATER FILTERS, HOME USE
WATER HAMMER NOISE DIAGNOSE & CURE
WATER ODORS, CAUSE CURE
WATER PUMP REPAIR GUIDE
WATER PRESSURE LOSS DIAGNOSIS & REPAIR
WATER SOFTENERS & CONDITIONERS
WATER TANK: USES, TROUBLESHOOTING
WATER TESTS, CONTAMINANTS, TREATMENT
WATER TREATMENT EQUIPMENT CHOICES
WELLS CISTERNS & SPRINGS
WELL CHLORINATION & DISINFECTION
WELL FLOW RATE
WELL WATER PRESSURE DIAGNOSIS
WELL YIELD IMPROVEMENT
WINTERIZE A BUILDING
Limitations of disinfection's ability to produce safe, potable drinking water: this article describes the limitations of relying only on disinfection (chlorine or other disinfectants) to make drinking water safe and potable.
We explain that some biological or pathogenic drinking water contaminants are either resistant to standard disinfection approaches such as chlorination while other water contaminants such as hazardous chemicals or particulates are simply not addressed by disinfection.
Our page top photo shows potable water being delivered to a storage cistern in San Miguel de Allende, Guanajuato, Mexico.
Green links show where you are. © Copyright 2015 InspectApedia.com, All Rights Reserved.
There is growing evidence that drinking water disinfection alone can be ineffective in adequately removing drinking water contaminants, both because of procedural errors (discussed here) and possibly because of persistant contaminant sources or contaminants that are partly-encapsulated inside water piping or containers, requiring extra contact time or additional cleaning and disinfection methods to assure a stable sanitary drinking water supply.
In August 2013 The New York Times reported that in the United States drinking water chlorination was first installed in a municipal water supply in Jersey City New Jersey and in Chicago in 1908, leading today to more than 53,000 water supply utilities in that country providing "some of the safest drinking water in the world".
But the article continued to point out that there is growing concern for the effectiveness of chlorination in adequately treating a variety of pathogens. - The New York Times, 27 August 2013
This is not a new water quality concern. Payment (1999) explain that residual chlorine present in drinking water distribution systems was not effective in reducing organisms other than E. coli. Here is an excerpt from the article abstract
More recently, Richardson (2003) noted that in addition to the pathogen resistance problem we've just noted, disinfection byproducts in drinking water are also hazardous. We discuss DBPs in more detail at
Lazarova (1999) pointed out that there was considerable variation in the effectiveness of chlorination as a water disinfectant depending on the beginning water quality:
LeChevallier (1999) explain that the turbidity of water affects its successful disinfection using chlorination:
Examples of Water Disinfection Limitations
Watch out: as we report throughout this article series, different disinfection methods vary in their effectiveness in combating different types of water contaminants. If you rely on a single disinfection method, for example chlorine disinfection, your water supply could still be contaminated by cryptosporidium, or if chemical contaminants are present, those, too, might remain.
Municipal water supplies are generally safe as their water treatment efficacy is monitored regularly as required by federal regulations. But private water supplies may be at risk.
Consulting with your local health department and local water testing laboratories can provide locally-accurate advice on what water tests are most important to perform in order to understand what water treatment may be necessary for your home or building.
Drinking water disinfection does not remove chemical contaminants
If the drinking water has been tested only for bacteria and subsequently treated only with disinfection, there is a risk that other contaminants may still be present in the water. In our experience this is partiularly the case if a private water well has become contaminated by ground water leaking into the well.
Groundwater or surface-runoff easily pick up surface contaminants such as road salt, pesticides, weed killers or other chemicals used above ground anywhere where these substances may be transported to a leak into a well.
Disinfectants that don't kill cysts
The Times article continued to note that following earlier disease outbreaks principally due to protozoan cysts of the parasite Cryptosporidium, the U.S. EPA added additional regulations requiring additional treatment for municipalities like New York city who were using un-filtered surface-reservoir water supplies.
New York City was reported to have instituted use of ultra voilet light to treat Cryptosporidium cysts that are otherwise resistant to just chlorination disinfection methods.
At BLEACH DISINFECTANT for DRINKING WATER we report as follows
Watch out: Bleach will not kill Giardia in typical drinking water disinfection methods such as those discussed here. While chlorine can kill Giardia cysts if used in high enough concentration and for sufficient contact time, typically the chlorine concentration in water necessary for Giardia would be too high for drinking purposes.
[Click to enlarge any image]
For this reason some municipalities where Cryptosporidium cysts are a concern add a water treatment step using chlorine dioxide. Others may use a combination of UV light and chlorine in the water treatment procedure. This treatment is also available to hikers, travelers, and for emergency water supply use.
Persistent Bacterial Sources in Water & Limitations of Chlorine Disinfection of Drinking Water
We have observed many instances of effective well shocking that resulted in a "passed" water test only to find that bacterial contamination has reappeared in the well water days or weeks after the well shock procedure. In these cases most often we suspet that there was a persistent bacterial source that was simply temporarily dealt-with by the disinfectant. Persistent bacterial water contamination sources might be
The New York Times article cited above pointed out that testing for coliform bacteria, the most common water "potability test" does not include testing for even other microorganisms such as methylobacteria, sphingomonads, mycobacteria, and the Giardia or Cryptosporidium cysts reported above. Bacteria located within protozoan cysts can survive in that form for literally hundreds of years if not effectively treated.
Schoenen (2002) pointed out that despite the use of chlorine disinfection of drinking water, water-bourne disease outbreaks have continued around the world, particularly where there are fecal contaminants in drinking water!
Previously Xu (1996) pointed out that pathogens entrapped in biofilms can limit the rate (and thus effectiveness) of chlorine disinfection:
Conversely, chlorine disinfection of drinking water may be more effective against some troublesome biological contaminants than previously thought: Shin (2000) discuss the resistance of a particular contaminant, norovirus, to chlorine disinfection of drinking water with a surprising result.
Water disinfectant effectiveness limited by water pH
We explain in this separate but important article that WELL DISINFECTANT pH ADJUSTMENT may also be necessary for effective water disinfection.
Continue reading at BLEACH DISINFECTANT for DRINKING WATER or select a topic from the More Reading links shown below.
Suggested citation for this web page
Green link shows where you are in this article series.
Frequently Asked Questions (FAQs)
No FAQs have been posted for this page. Try the search box below or CONTACT US by email if you cannot find the answer you need at InspectApedia.
Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.
Search the InspectApedia website
HTML Comment Box is loading comments...
Technical Reviewers & References